$2 THE HUMAN MOTOR 



in a thermal motor, a very slow movement of the pistons, almost 

 in equilibrium (conditions of reversability) and an absence of 

 calorific loss, is purely theoretical, it leads to the expression : 



R -IZI!'-1-..L' 



J-Mnax r> * * i 



the absolute temperatures T and T' being those of the hot source 

 (the boiler) and the cold (the condenser). The value Rmax is 

 an ideal, but impossible, value. Carnot only wished to demon- 

 strate that a fraction, always lower than unity, -represents the 

 maximum yield in useful work of the expended energy. This 

 disposed the idea of perpetual motion, but his theoretical re- 

 searches went beyond such a limited object as has been shown 

 ( 35). 



Further, internal combustion engines do not fulfil the condition 

 of reversability, because the gases, having exploded and changed 

 their "composition, cannot resume their initial state. It follows 

 that Carnot's question of yield never occuis, and cannot occur, 

 if a change of chemical state or combustion takes place in the 

 cycle and makes it irreversable. This is what takes place in the 

 internal operations of the muscles, as Clausius showed Hirn^ 1 ) 

 at the beginning of his thermcdynamic studies. 



The gross yield, r, of a thermal engine varies from 7 to 14 per 

 cent. In exceptional circumstances, D welsh auvers-Dery ob- 

 tained 23 per cent., with a " superheat " of 430, 



T == 430 + 273 = 703. 



In internal combustion engines a very high temperature is pro- 

 duced, and by combining the compression of the mixture with a 

 very high temperature, gross yields of 30 to 40 per cent, can be 

 obtained : as in the Diesel engine. 



Some trials on a gas engine of 6'73 H.P. have given the follow- 

 ing results : ( 2 ) 



Heat transformed into indicated work ...... 18'70 per ce nt. 



,, lost by radiation ............ 7'50 



,, ,, by cooling of the cylinders ... ... 46*00 ,, 



,, by the exhaust gases ......... 27*80 



100-00 



Organic yield : 73'6% ; from which a gross yield is obtained 

 of 



70.7 

 r = 18-70 X = 13-76%. 



(*) Him, Recherches sur I' Equivalent mtcanique de la chaleur, followed by 

 Rapport of Clausius, Colmar, 1858, p. 138. 

 ( a ) Ginie Civil of 24th November. 1906. 



